Average of the previous twelve months

Hi,

I'd like to know whether it's possible to calculate the average on a ratio (for example kgs of the stock) always of the previous 12 months.

For example, if we are in 03.2015 we should calculate the average from 04.2014 to 03.2015.

An example:

FISC/PER    KG                AVERAGE

=============================

01.2014        12                 12

02.2014.       32                 22

03.2014        43                 29

04.2014.       65                 38

05.2014        112               52,8

06.2014.                           52,8

07.2014       12                  46

08.2014.      56                 56

09.2014                            47,43

10.2014.      87                 52,38

11.2014       32                 50,11

12.2014.      67                 51,80

01.2015       98                 60,40

03.2015.                           63,56

Can anybody help me?

Thanks in advance.

Regards.